Wendy's is investigating reports of "unusual activity" on payment cards that had been used at some of its restaurants.

The company said it learned from payment industry contacts this month of reports indicating fraudulent charges may have occurred on cards that had been used legitimately at some of its locations. Wendy's said it has launched an investigation with the help of cybersecurity experts and that it is cooperating with law enforcement officials.

"Until this investigation is completed, it is difficult to determine with certainty the nature or scope of any potential incident," the company said.

Wendy's Co., based in Dublin, Ohio, encouraged customers to watch for unauthorized charges on their cards.

The investigation was first reported by the website KrebsOnSecurity on Wednesday.